1. Field of the Invention
This invention relates to a heat treatment method in which such material as a semiconductor substrate (hereinafter referred to as "wafer") is heat-treated by irradiating both front and back sides thereof with light, and more particularly to a heat treatment method by which a heat treatment is uniformly applied to every wafer when a plurality of wafers are taken in a heating furnace one by one and heat-treated therein.
2. Prior Art
Generally, the heat treatment process of the wafer is widely used in varieties of heat treatments, i.g., a heat treatment for activating and uniformly composing an ion implanted layer as an after-treatment of ion implantation, a heat treatment for stabilizing a silicon film, etc.
In any of these heat treatments, it is required for every surface of the wafer including front and back sides thereof to be uniformly heated, and accordingly in view of rapid heat treatment, in case of using such heating means as halogen lamp for the irradiation with light, it is indispensable to secure uniformity of irradiation applied from such heating light source to the wafer.
As for the method of securing said uniformity in the distribution of irradiation, it is well known so far that, as is disclosed in Japanese laid open Patent Publication (unexamined) Sho 57-147237, a wafer accepted in a heating furnace is horizontally carried in relation to the light source, otherwise the wafer is horizontally carried at specified amplitude.
In case of securing the uniform irradiation by using such method, however, there exists such problem that, at the time immediately after starting the heat treatment operation, i.e., when the atmosphere in the furnace has not been uniformly heated yet, a result of heat treatment (annealing effect) of the first one of the prearranged wafer is different from that of the following several wafers, which is a serious problem in view of product quality.
As for the method of controlling the atmosphere in the furnace at required temperature, several attempts have been proposed as disclosed in Japanese laid open Patent Publication (unexamined) Sho 53-120075 or Sho 58-70536.
Further, the applicant has already proposed a heat treatment method by filing a Japanese Patent Application Sho 59-105571 wherein the furnace is preliminarily heated before an object to be heat-treated is placed in the furnace based on an output program for controlling the output of the light source which is preliminarily stored in a memory.
According to the methods disclosed in aforementioned Publications Sho 53-120075 and Sho 58-70536, in the event of shutting down the heat treatment operation for long period and restarting it afterward, there arises such disadvantage that the annealing effect, i.e., product quality of the wafer heat-treated before the shutdown is different from that of the wafer heat-treated after the restarting.
Aforementioned Japanese Patent Application Sho 59-105571 was filed for the purpose of solving the above-discussed disadvantage.